1. Field of the Invention
The invention relates to a vehicle seat headrest assembly with an adjustable portion for supporting the head of a seat occupant during a vehicle crash event.
2. Background Art
Contemporary automotive vehicles have driver and passenger vehicle seats facing in a forward vehicle travel direction. The vehicle seats each include a seat back portion and a seat cushion portion. A headrest assembly is situated at the upper margin of the seat back portion at a location directly adjacent the head of a vehicle occupant. In the event of a vehicle rear-end crash in which a forwardly directed high impact inertia force is created, a forwardly directed component of the inertia force will be distributed directly to passenger seat supporting structure, which is secured to the vehicle body and chassis. This forward component of the impact force is transferred through the vehicle body and chassis to the headrest assembly. The headrest assembly is intended to support the head of the seat occupant in order to prevent so-called whiplash injury caused by a crash event.
It is known design practice to provide a headrest adjustment mechanism for adjusting the headrest in a forward direction relative to the seat back during a vehicle rear-end crash event in order to prevent the head of a vehicle occupant from sudden rearward motion relative to the headrest assembly, thereby reducing the possibility of whiplash injury. Examples of adjustable headrests of this type may be seen by referring to U.S. Pat. Nos. 7,111,901 and 7,070,235.
Because of elasticity of the body and chassis structure and the seat frame, the inertia of the body and chassis structures and the elasticity of the seat frame and linkages between the seat frame and the adjustable headrest, a time delay exists between the instant a rear impact occurs during a vehicle crash and the instant the inertia forces are transmitted to the headrest assembly. For this reason, an adjustable feature of a headrest assembly of known design may be inadequate to protect a vehicle occupant from injury.